1. Field of the Invention
This invention is directed to electrical circuit breakers, and more particularly to electrical circuit breakers which include a manual mechanism for tripping the circuit breaker.
2. Background Information
Circuit breakers are generally well-known in the art. Examples of molded case circuit breakers are disclosed in U.S. Pat. Nos. 4,698,606; 4,725,800; and 4,963,846. Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit condition.
Molded case circuit breakers include at least one pair of separable contacts which generally may be operated manually by way of an operating handle disposed on the outside of the case or automatically in response to an overcurrent condition. When the circuit breaker is on, a movable contact assembly is in contact with a stationary or fixed contact assembly. The closed contacts conduct a flow of current between a line terminal and a load terminal. When the circuit breaker trips or is switched off, the movable contact assembly is moved away from the fixed contact assembly, thus, interrupting the flow of current between the line and load terminals.
Circuit breakers generally include a pivoting operating handle, which projects through an opening formed in the breaker housing, for normal on/off manual operation. The operating handle generally assumes three or more positions during operation of the circuit breaker. When the handle is moved to the ON position, and the breaker is not tripped, the contacts of the circuit breaker close, thereby allowing electrical current to flow between a current source and an associated electrical circuit. When the handle is moved to the OFF position, the contacts of the circuit breaker open, thereby preventing current from flowing through the circuit breaker. When the circuit breaker trips, and the separable contacts thereof are opened, the handle moves to a TRIP position between the ON and OFF positions.
Molded case circuit breakers have mounted within their housing an operating mechanism and a trigger or latching assembly which, under normal conditions, latches the operating mechanism operatively coupled to one or more main contacts. The operating mechanism of the circuit breaker is designed to rapidly open and close the separable contacts, thereby preventing a moveable contact from stopping at any position which is intermediate a fully open or fully closed position. Actuation of the latching assembly unlatches the operating mechanism which causes the contacts to separate, thereby interrupting the flow of current through the circuit breaker between the line and load terminals.
Some types of circuit breakers include an electro-mechanical trip unit which interrupts current flow in two or more modes of operation. The electro-mechanical trip unit generally senses overload currents of up to about five to six times normal rated current as well as short circuit currents of greater than about ten times normal rated current. A bimetal member is disposed in series with the separable contacts. In the first mode of operation, with the occurrence of an overload current, the bimetal member is heated. In turn, the bimetal member deflects and engages a flange of a trip bar, thereby rotating the trip bar and tripping the circuit breaker. An electromagnet is also disposed in series with the separable contacts as part of the electrically conductive path between the line and load terminals. In the second mode of operation of the electro-mechanical trip unit, in response to a short circuit current, the electromagnet is energized and electromagnetically attracts the armature thereto. In turn, the armature rotates and engages another flange of the trip bar, thus, rotating the trip bar and tripping the circuit breaker.
It is known to electrically interconnect an external shunt trip mechanism, ground fault trip mechanism or undervoltage trip relay with an internal solenoid of the circuit breaker. Whenever this solenoid is energized, a plunger thereof drives the armature of the electro-mechanical trip unit in order to trip the circuit breaker.
Other types of circuit breakers may include an electronic trip unit for automatically interrupting the current flow. The electronic trip unit includes current sensors or transformers which respond to an overcurrent condition. When the overcurrent condition is sensed, the current sensors provide a signal to the electronic circuitry within the electronic trip unit which energizes a solenoid. In turn, a plunger of the solenoid engages a flange of the trip bar which rotates, unlatches the operating mechanism and trips the circuit breaker. It is also known to drive the armature of the electro-mechanical trip unit with the plunger of the solenoid in order to trip the circuit breaker.
Circuit breakers may also include a manual pushbutton for manually interrupting the current flow. Whenever the pushbutton is pressed, a plunger associated with the pushbutton engages a flange of the trip bar. This flange rotates the trip bar, thereby unlatching the operating mechanism and tripping the circuit breaker. The manual pushbutton facilitates partial testing of the trip mechanism. The manual pushbutton, also, provides for a relatively rapid manual trip operation under emergency conditions in comparison to the normal manual ON to OFF operation with the operating handle. However, there is room for improvement of the manual pushbutton.
There is a need, therefore, for a manual trip mechanism which facilitates additional testing of the circuit breaker.
There is a more particular need for such a mechanism that facilitates such testing without significantly decreasing the reliability of the manual trip mechanism.
There is another need for a mechanism which provides manual trip with minimal modification of an existing circuit breaker.
There is a more particular need for such a mechanism that provides manual trip with minimal cost.